PC Games Hardware has a response from NVIDIA to a recent statement by ATI that developers other than Epic use PhysX for physics "because they’re paid to do it." NVIDIA's Nadeem Mohammed, Director of Product Management, PhysX, who says: "we do not pay developers to select PhysX instead of other physics solution." He also states that PhysX is not proprietary, even though it obviously is, saying: "PhysX is a complete Physics solution which runs on all major platforms like PS3, XBOX360, Wii, PC with Intel or AMD CPU, and on the PC with GeForce cards; it even runs on iPhone. It's available for use by any developer for inclusion in games for any platform - all free of license fees. There's nothing restrictive or proprietary about that."

PhysX is a piece of shit and has been from its inception. I don't know if Nvidia's made it any better, I haven't really had many games to try it out, but I hope that this statement is true, that they don't pay developers to choose PhysX. (Though I'm 99% convinced they are.)